The present invention relates to a unique and novel rotor and bearing system for an energy conversion machine, and more specifically to the placement of rotors and bearings within a turbomachine.
A turbomachine is an energy conversion machine. Typically a turbomachine can generate electric power and may include a compressor, turbine, gears, motors, and generators. In general, such a system includes one or more rotors supported on one or more bearings enabling free rotation of the shafts which carry the compressor wheel, turbine blades and permanent magnet rotor, or sleeve.
In high efficiency turbomachines such as those describes in U.S. Pat. Nos. 5,752,380 and 5,685,156, the efficiencies of the machines are substantially enhanced by the use of thrust and journal bearings of the compliant foil hydrodynamic fluid film type. Examples of these bearings are described in U.S. Pat. No. 5,427,455 and U.S. Application Publication No. 2002/0054718.
A turbomachine having three journal bearings and one thrust bearing is described in U.S. Pat. No. 5,697,848. The machine described in U.S. Pat. No. 5,697,848 is generally designed for kilowatt output (in the 30 KW range) and, for commercial efficiencies, is designed to be small, compact and easily transportable. Such machines have traditionally included journal bearings on either end of the permanent magnet shaft of the turbo generator. The powerhead of these turbomachines includes a compressor and turbine mounted on a shaft supported by a journal bearing and a thrust bearing positioned within the powerhead housing between the compressor and the turbine.
The conventional journal bearing includes stationary metallic foils positioned in close proximity to the rotating shaft. Additionally, the conventional thrust bearing includes a flange sandwiched between thrust bearings which are designed to restrict motion, counteract thrust loads, and dampen the transfer of vibratory thrust. These thrust bearings allow for thrust balancing and axial positioning of the permanent magnet shaft and the powerhead shaft. As such, the prior art positions at least one journal bearing and at least one thrust bearing between the compressor and turbine of the powerhead section.
The size and efficiency of these smaller prior art machines allow both the journal bearing and thrust bearing to be mounted between the compressor and the turbine. This is due to the controllable level of heat generated by the smaller overall design of these conventional systems. The present materials technology can design cost effective metal bearings that withstand the heat levels generated in the combustion chamber that power these smaller turbines. However, even in these smaller systems, the tremendous heat generated in the combustion chamber impacts the longevity of the journal and thrust bearings mounted adjacent the turbine. As such, those journal and thrust bearings can be the first components to fail in these machines because of their exposure to these heat levels.
Also, the configuration of the bearings and rotors in the prior art machines substantially block gas flow from the compressor to the bearings and on to the turbine. As such, without additional gas passages, or channels designed into the prior art machines, proper gas transfer from the compressor to the bearings and the turbine is not accomplished. Additionally, with the use of the gas passages that bypass the bearings, the natural convective cooling activity of the gas flow is not imparted to the bearings. These facts combined with the location of the thrust bearing and journal bearing near the combustion areas in the prior art turbomachines results in high operating temperatures for those prior art bearings. As such, these prior art bearings must be made of more expensive materials that tolerate high temperatures. Even then, these bearings in the prior art systems have a tendency to fail, break down, and malfunction.
It is also known, as is described in U.S. Pat. No. 5,697,848, to completely support the generator/motor rotor on gas bearings and to provide a flexible coupling between the permanent magnet shaft and the powerhead shaft. The flexible couplings transmit all torque from one rotor to the other, but radial excursions of one rotor generally do not affect the motion of the other rotor.
As discussed above, again as is illustrated in the U.S. Pat. No. 5,697,848, the powerhead shaft is carried by a journal bearing and a thrust bearing mounted between the compressor and the turbine. In larger machines, for example in a 200 kilowatt machine, the inventors have found that the extreme heat generated in the combustion chamber of the machine will exacerbate problems associated with the thrust bearing directly adjacent the hot section of the machine. The inventors have developed a unique and novel rotor and bearing system which alleviates these problems.